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An article in the Kansas City Star warns that the edge of totality,
depicted with great precision on eclipse maps, should not be taken as
the literal truth. One uncertainty is the Sun's semidiameter. There is a
feeling among some astronomers that the Sun is a little bigger than its
official IAU radius of 696,000 km.

"Anyone who has been using online maps to decide where they intend to
view the historic Aug. 21 total eclipse of the sun may want to take
another look.

"Those maps, provided by NASA and others, show a crisply defined,
70-mile-wide path of totality where the moon will block 100 percent of
the sun. But they are not as precise as they appear, at least on their
edges.

"Xavier Jubier, a French engineer whose calculations have been used to
create the interactive Google maps of the eclipse, confirmed to The Star
by email that the actual path of the totality is slightly narrower than
the 70 miles shown on current maps.

"Jubier said that the current maps are accurate using the
696,000-kilometer radius and other standards agreed upon in 1976 at a
meeting of the International Astronomical Union.

"'This is perfectly accurate but we know it does use a solar diameter
that is not large enough. Why don’t we change the value(?)' Jubier
wrote. 'Well simply because the IAU (International Astronomical Union)
has not yet approved a new value. This is part of the research we’re
doing and for which we’re looking for funding.'

"He continued, 'So technically speaking if the Sun is larger than the
adopted IAU value, and we know it is, the eclipse path is necessarily
narrower and our tools can simulate this, yet the standard maps for the
public will still retain the currently adopted solar radius until a new
value has been accepted. Such a process will take years as everything
needs to be peer-reviewed and then validated during a General Assembly.'"

http://www.kansascity.com/news/local/article166394247.html

In practice I don't think this will be an issue, since anyone near the
edge will naturally move toward the central line in order to get a
longer totality.

   

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